Acardiacus acephalus twinning associated with exomphalos major, high impeforate anus and hypospadias

Introduction

Acardiac twinning was first described by Benedetti in 1533 [5]. This is associated with a panoply of anomalies, probably due to reversed foetal blood flow [17]. The disruption of normal development is thought to be caused by the pumping of oxygen and nutrient poor blood from the normal ‘pump’ twin to the acardiac twin. This causes disrupted development of the cranial end (brain and heart) [7], while the caudal end survives and is subclassified based on the remnant anatomy [3]. Twin reverse arterial perfusion (TRAP) syndrome was proposed as another cause of acardiac twinning as described by Van Allen et al. [17]. Acardiac twins result from monozgotic twinning with three anatomic abnormalities: (i) disturbed foetal cardiac development; (ii) artery-artery anastomosis carrying blood from the normal twin to the acardiac; (iii) vein to vein anastomosis carrying blood from the acardiac twin to the normal twin.

Scahtz suggested that omphalocele caused obstruction to the venous return, and thus, caused the acardiac twinning.

Case report

A 19-year-old primigravida presented with a pregnancy in which an antenatal ultrasound scan at 12 weeks showed a foetus with gastroschisis, findings that were confirmed on repeat scans. A magnetic resonance imaging (MRI) scan suggested, in addition to the abdominal wall defect, a suspected cervical teratoma (Figure 1). Neither the ultrasound scan nor the MRI scan suggested twinning. Elective caesarean was planned at 37 weeks, however, the mother presented in spontaneous labour at 35 weeks of gestation. Preparation was made for an ex utero intrapartum (EXIT) procedure to secure the infant’s airway prior to clamping the umbilical cord. Twin male infants were delivered, sharing a single placenta, one of which was rudimentary. Both twins exhibited exomphalos major Figures 2 and 3.

Figure 1

Maternal MRI scan (antenatal).

Figure 2

Intraoperative photograph.

Figure 3

Post operative image.

Further examination revealed the fully formed twin to have an imperforate anus and a hypospadias. He also had a tubular structure running along the anti-mesenteric border of the extruded colon. The rudimentary acardiac twin had two partially formed lower limbs and rudimentary genitalia Figure 4. An abdominal wall defect in the malformed twin was seen with extruded viscera.

Figure 4

X ray showing rudimentary limbs.

After initial stabilisation, the twins were taken to theatre. A large ruptured membrane was attached to the umbilicus of the relatively normal ‘pump’ twin, suggestive of a ruptured exomphalos. The herniated bowel of this twin was communicating with the bowel of the acardiac twin through a small fistula at the terminal ileum of the normal twin. The acardiac twin was resected with its herniated bowel and umbilical cord. The pump twin had its abdominal defect closed and a defunctioning loop sigmoid colostomy formed in the left iliac fossa.

Post-mortem X-ray of the acardiac twin showed the presence of two femori and rudimentary tibiae (Figure 5). Histopathology showed presence of a well-formed bowel, a kidney that showed large dilated spaces and an adrenal gland.

Figure 5

Line diagram.

The surviving twin underwent subsequent imaging via the distal loop of the colostomy that demonstrated a rectovesical fistula. The infant underwent a laparotomy assisted posterior sagittal anorectoplasty at the age of 4 months, where the presence of a recto-bladder neck fistula was confirmed. The defunctioning colostomy was closed at 8 months of age.

Discussion

The incidence of acardiac twinning has been quoted as 1 in 34,600 deliveries [4]. There is a female predominance in acardiac twins and their normal twin counterparts [1].

Acardiac twinning occurs as a result of a monochorionic gestation with a disrupted foetal to placental blood flow from the two twins. Placental anastomoses are rare in polyzygotic twinning, therefore, acardiac twins are usually monozygotic. As a result of a pressure differential, reversed perfusion occurs due to chorionic plate arterioarterial and venovenous anastomosis with the other twin. De-oxygenated blood from the normal twin enters the other twin through a single umbilical vessel. As this blood enters the affected twin through the iliac circulation, the foetus develops inappropriately.

The classification system of the acardiac twins includes four types [2]: (i) acardiacus acormicus (acormis) – a head only, exceedingly rare; (ii) acardiac anceps (aceps, paracephalus) – head is present but poorly developed; (iii) acardiacus acephalus (omphalus) – trunk and legs alone present; head and upper extremities are absent; (iv) acardiacus amorphous (anideus, cryptomorphus) – no recognizable anatomy. A further 5^th subtype was added by Simmonds and Gowen [14]: (v) acardiacus mylacephalus – amorphous mass with development of one or more limbs.

The criteria for acardiac twinning have been suggested by Spencer as the following: (i) enclosure in an amniotic sac; (ii) covered by normal skin; (iii) grossly recognizable anatomic parts; (iv) attached to the placenta by an umbilical cord and with placentovascular anastomosis to the autosite [15].

To our knowledge, this is the first report of an acardiac twin with externalized intestine, with the normal twin having an anorectal malformation, hypospadias and an abdominal wall defect.

Completely externalized intestine in an acardiac twin has been described previously [3]. Omphalocele with an acardiac twin has been described in case reports but there has been no mention of the incidence. Napolitano and Screiber in a review of 151 cases, which also contained a report of an acardiac with omphalocele, did not have a mention of the frequency of omphalocele [8]. Lachman et al. [5] have described in detail the anatomic organs in 61 cases of acardiac twins.

Obladen described the recent advances in management [9]. The prenatal ultrasound appearance has been described by Lehr and DiRe in 1978 [6] and Pretorius et al. documented the reverse arterial perfusion pattern with colour Doppler [11].

Interventions aimed at rescuing the normal ‘pump’ twin have been described by Robie et al. [13], who first delivered the acardiac twin by hysterotomy at 22 weeks and delivered the pump twin at 33 weeks successfully. Porreco et al. described percutaneous cord occlusion by coil embolization. A platinum coil was put in the single umbilical artery of the acardiac twin with successful interruption of flow [10]. In 1994, Quintero et al. successfully ligated the umbilical cord fetoscopically at 19 weeks. The normal twin was successfully delivered at 36 weeks and had a benign postnatal course [12]. Radiofrequency ablation had also been used to block the circulation of the acardiac twin. Tsao et al. have reported 12 out of 13 twins surviving between 1998 and 2001 [16].